The present invention relates to a device for correcting a composition of fuel-air mixture upon a change in the state of load of an internal combustion engine with which a mixture-forming device is associated.
In gasoline-operated internal-combustion engines the composition of the fuel-air mixture (lambda value) must be maintained--independently of the operating point of the engine at the time--within narrow limits in order to obtain operation which is low in injurious substances. Only in this way is it possible to comply with the legally permitted limit values for pollutants in the exhaust gas of the engine. Particularly when the engine is operating with exhaust-gas catalysts, the "lambda window" should vary only very slightly around an optimal lambda value for optimal conversion of the composition of the mixture. This is obtained customarily by:
A pre-control of the fuel-air mixture for the entire operating range of the engine which differs from the very start only as little as possible from the ideal mixture composition and in practice is effected as a general rule by the calling up of specific data of engine-performance characteristics determined by tests;
An additional control regulation of the precontrolled mixture by means of a lambda probe which effects a return to the ideal lambda value in the event of deviations of the composition of the mixture from the ideal value.
The less the lambda value of the pre-controlled mixture differs from the ideal lambda value, the more effective the control of the fuel-air mixture by the lambda probe can be carried out in order to reduce fuel pollutants contained in the exhaust gas.
Upon the operation of an internal-combustion engine, it can be noted upon every change of the state of load that the air pressure varies in the inlet pipe. In this way:
Upon a reduction of the pressure in the inlet pipe, fuel which has deposited on the wall of the inlet pipe in the form of a film of fuel is evaporated and the fuel/air mixture behind the mixture-forming device is make richer, i.e. the lambda value is reduced;
Upon an increase in the pressure in the inlet pipe, fuel is precipitated on the inlet pipe and thus the mixture entering the engine becomes leaner, i.e. the lambda value increases.
In both of these cases, the fuel/air mixture fed the engine differs to a greater or lesser extent from the lambda value necessary for the optimal conversion. The faster the change in the load on the engine takes place, the greater the deviation from the optimal lambda value will be. The change in the pressure of the inlet pipe takes place upon changes in load of the engine, in particular, by change in position of the control member which regulates the amount of mixture, for instance a throttle valve, a throttle cone, etc.
In one known mixture-forming device, the resultant fuel/air mixture which is produced in the mixture-forming member which is arranged centrally on the inlet pipe differs only slightly from the ideal composition even without control. By a variable wetting of the inlet pipe, particularly in the case of rapid changes in load, a mixture which deviates from the ideal mixture is, however, fed to the engine and the quality of the exhaust gas is thus impaired. The faster the inlet-pipe pressure changes upon change in load of the engine, the less it is possible, by control via the lambda probe, to adjust these deviations from the ideal lambda value to the lambda value necessary for optimal conversion.